Photoreactivity improvement of TiO 2 /Sr 4 Al l4 O 25 :Eu,Dy heterojunction photocatalyst by Fe doping and annealing in N 2 –H 2 mixed gas

Sr 4 Al l4 O 25 :Eu,Dy phosphor beads were impregnated with Fe, followed by TiO 2 sol–gel coating. The heat treatment atmospheres after TiO 2 coating were N 2 , N 2 –H 2 mixed gas, and air. X-ray diffraction, scanning electron microscopy, and energy dispersive analysis confirmed the crystallinity, spherical nano-TiO 2 morphology, and elemental composition of the Fe-doped TiO 2 /Sr 4 Al l4 O 25 :Eu,Dy phosphor beads. X-ray photoelectron spectroscopy analysis verified the existence of oxygen-deficient Ti δ+ due to the Fe doping and reducing atmosphere. Additionally, the thermal treatment of Sr 4 Al 14 O 25 :Eu,Dy/TiO 2 beads in the N 2 –H 2 reducing atmosphere enhanced N doping in the TiO 2 matrix. The red shift of the diffuse absorption spectra increased with the amount of Fe doped on phosphor, indicating heterojunction narrowing in Sr 4 Al 14 O 25 :Eu,Dy/Fe-TiO 2 . Photoluminescence emission deteriorated with increasing Fe doping and N 2 heat treatment. However, the N 2 –H 2 mixed gas preserved up to 90% of the photoluminescence intensities regardless of the amount of Fe dopant on the phosphor/TiO 2 bead surface. The photoreactivity performance was evaluated using a toluene volatile organic compound as pollutant under 30 lx ultraviolet (UV) and 1200 lx visible light sources. The 0.06 M Fe-impregnated Sr 4 Al 14 O 25 :Eu,Dy/TiO 2 beads heat treated in a N 2 –H 2 reducing atmosphere exhibited outstanding photocatalytic activity of up to above 95% for 60 min in both UV and visible light activated reactions. Moreover, the 0.06 M Fe-doped Sr 4 Al 14 O 25 :Eu,Dy/TiO 2 phosphor beads demonstrated plausible reusability with photocatalytic efficiencies above 90% in five repeated test cycles.